Fire suppression system with freeze protection

ABSTRACT

A water and inert gas fire suppression system ( 10 ), and method for extinguishing a fire in a protected space are provided with a simple and inexpensive freeze protection mechanism. To prevent the water, or other liquid fire extinguishing agent, entrained in the inert gas flow from freezing during transport through the inert gas distribution network ( 15, 15   a,    15   b,    17, 19 ) a secondary liquid is introduced into the inert gas flow and then removed from the inert gas flow upstream of the discharge of the two-phase water and inert gas flow into the space being protected. The inert gas is heated by means of the thermal inertia (TI) of the secondary liquid, which may be excess amount of water or an amount of another liquid having a thermal inertia (TI) at least equal to that of water.

FIELD OF THE INVENTION

This invention relates generally to fire suppression systems. Moreparticularly, this' invention relates to freeze protection in a firesuppression system using water as a liquid fire extinguishing agententrained in a pressurized inert gas.

BACKGROUND OF THE INVENTION

Fire suppression systems are commonly used in commercial buildings forextinguishing fires. In one type of fire suppression system, a jet ofliquid fire extinguishing agent, commonly water from a water supplytank, is injected into a high velocity stream of pressurized inert gasfrom an inert gas storage tank as the inert gas is passing through adelivery pipe communicating with a network of distribution pipes. Uponinteraction of the high velocity stream of inert gas with the water jet,the water droplets in the water jet are atomized into a mist of verysmall or minute droplets, typically having a median droplet size rangingbetween 5 and 60 micrometers, thereby forming a two-phase mixture ofwater mist droplets entrained in and carried by the inert gas stream.This two-phase mixture is distributed via the network of distributionpipes to a plurality of spray nozzles mounted to the distal ends of therespective distribution pipes. The spray nozzles spread the water mistdroplets and inert gas over a desired area to in effect flood that areawith water mist droplets and inert gas for extinguishing a fire in theprotected volume.

The inert gas commonly used in conventional inert gas fire suppressionsystems is nitrogen, but argon, neon, helium or other chemicallynon-reactive gas, or mixtures of any two or more of these gases may beused. The inert gas suppresses fire within the protected volume byincreasing the heat capacity per mole of oxygen and diluting the oxygencontent within the protected area. Additionally, the water mist dropletsenhance fire suppression by also raising the overall heat capacity ofthe atmosphere within the protected volume. Due to the presence of thewater droplets, the two-phase mixture of water mist droplets and inertgas has a higher overall heat capacity than the inert gas alone.Consequently, the two-phase mixture of water mist droplets and inert gaswill more effectively absorb heat from the flame sheath to the pointthat the temperature of the gas within the vicinity of the flame sheathdrops below a threshold temperature below which combustion can not besustained, for example below 1800 degrees C.

International Patent Application No. PCT/GB02/01495, published asInternational Publication WO02/078788, for example, discloses a waterand inert gas fire and explosion suppression system of the typehereinbefore described.

A potential concern associated with such systems is freezing of thewater droplets as the two-phase mixture passes through the network ofdistribution pipes. As the inert gas passes from the supply cylinders tothe spray nozzles, the inert gas expands as the pressure drops from thesupply pressure of 200 to 300 bars to atmospheric pressure. Thisadiabatic expansion of the inert gas causes a cooling of the inert gasthat may generate temperatures in the range of −60 degrees C. to −100degrees C. Such extreme temperatures may result in a significant amountof the water droplets freezing as they traverse the network ofdistribution pipes. Since frozen water droplets attach to the pipe wallsthey will not take part in extinguishing a fire, if a sufficient degreeof freezing of water droplets occurs, the fire suppression effectivenessof the system will be degraded.

SUMMARY OF THE INVENTION

A fire suppression system and method for extinguishing a fire in aprotected space are provided with a simple and inexpensive freezeprotection mechanism.

In an aspect of the invention, the method for extinguishing a fire in aprotected space includes the steps of: passing a flow of inert gaseousfluid to at least one discharge device operatively associated with theprotected space; introducing a first amount of liquid fire extinguishingagent into the flow of inert gaseous fluid upstream of the at least onedischarge device; introducing a second amount of a secondary liquid intothe flow of inert gaseous fluid for heating the flow of inert gaseousfluid; and removing the second amount of the secondary liquid from theflow of inert gaseous fluid upstream of the at least one dischargedevice. In an embodiment, the liquid fire extinguishing agent compriseswater, although the method may be used in connection with any liquidfire extinguishing agent that may be susceptible to freezing due toexposure to the inert gas flow.

In an embodiment of the method, the step of introducing a second amountof a secondary liquid into the flow of inert gaseous fluid comprisesintroducing a second amount of water into the flow of inert gaseousfluid. The first amount of water and the second amount of water may beintroduced into the flow of inert gaseous fluid as a single amount ofwater. The step of removing the second amount of the secondary liquidfrom the flow of inert gaseous fluid upstream of the at least onedischarge device comprises removing a desired portion, in an embodimentabout one-half, of the single amount of water introduced into the flowof inert gaseous fluid upstream of the at least one discharge device.The second amount of water may be introduced into the flow of inertgaseous fluid at about room temperature or may be heated to a desiredtemperature before introduction into the flow of inert gaseous fluid.

In an embodiment of the method, the step of introducing a second amountof a secondary liquid into the flow of inert gaseous fluid comprisesintroducing a second amount of a secondary liquid having a thermalinertia at least equal to that of water at room temperature into theflow of inert gaseous fluid upstream with respect to the flow of inertgaseous fluid of introducing a first amount of water into the flow ofinert gaseous fluid. The thermal inertia of the secondary liquid isindicative of its resistance thermal change and is defined hereinafteras the product of the specific heat capacity of the secondary liquid andthe temperature differential between the secondary liquid storagetemperature and the freezing point temperature of the secondary liquid.In an embodiment of the method, the step of introducing a second amountof a secondary liquid into the flow of inert gaseous fluid comprisesintroducing a second amount of a secondary liquid having a specific heatcapacity at least about equal to the specific heat capacity of water anda freezing point temperature less than 0° C. into the flow of inertgaseous fluid upstream with respect to the flow of inert gaseous fluidof introducing a first amount of water into the flow of inert gaseousfluid. The step of removing the second amount of the secondary liquidfrom the flow of inert gaseous fluid upstream of the at least onedischarge device may comprise removing the secondary liquid from theflow of inert gaseous fluid upstream with respect to the flow of inertgaseous fluid of introducing a first amount of water into the flow ofinert gaseous fluid and downstream with respect to the flow of inertgaseous fluid of introducing a second amount of a secondary liquid intothe flow of inert gaseous fluid.

In an embodiment of the method, the step of introducing a second amountof a secondary liquid into the flow of inert gaseous fluid comprisesintroducing a second amount of a secondary liquid into the flow of inertgaseous fluid upstream with respect to the flow of inert gaseous fluidof introducing a first amount of water into the flow of inert gaseousfluid, and the step of removing the second amount of the secondaryliquid from the flow of inert gaseous fluid upstream of the at least onedischarge device comprises removing the secondary liquid from the flowof inert gaseous fluid downstream with respect to the flow of inertgaseous fluid of introducing a second amount of a secondary liquid intothe flow of inert gaseous fluid and upstream with respect to the flow ofinert gaseous fluid of introducing a first amount of water into the flowof inert gaseous fluid. In an embodiment, the secondary liquid comprisesa saturated solution of potassium lactate.

In an aspect of the invention, the fire suppression system includes asource of pressurized inert gaseous fluid, at least one fluid dischargedevice disposed in operative association with the protected space, aninert gas distribution network for directing a flow of the inert gaseousfluid from the source of pressurized inert gaseous fluid to the at leastone discharge device for emission into the protected space, and a sourceof water, the source of water connected in fluid flow communication withthe inert gas distribution network for introducing water from the sourceof water into the flow of, inert gaseous fluid. Additionally, the systemincludes a source of a secondary liquid having a relatively high thermalinertia for heating the flow of inert gaseous fluid, the source of thesecondary liquid connected in fluid flow communication with the inertgas distribution network for introducing the secondary liquid into theflow of inert gaseous fluid, and a liquid capture vessel for removingthe secondary liquid from the flow of inert gaseous fluid, the liquidcapture vessel connected in fluid flow communication with the inert gasdistribution network downstream with respect to the flow of inertgaseous fluid of the connection of the source of a secondary liquid tothe inert gas distribution network and upstream with respect to the flowof inert gaseous fluid of the at least one fluid discharge device.

In an embodiment of the system, the secondary liquid comprises water.The source of water and the source of a secondary liquid may be a singlesource. With water as the secondary liquid, the liquid capture tankremoves a desired portion of the water introduced into the flow inertgaseous fluid from the flow of inert gaseous fluid with entrained waterupstream with respect to the flow of inert gaseous fluid of the at leastone fluid discharge device. In an embodiment, a flow splitter isdisposed in the inert gas distribution network downstream with respectto the flow of inert gaseous fluid of the connection of the singlesource of water to the inert gas distribution network and upstream withrespect to the flow of inert gaseous fluid of the liquid capture vessel,the flow splitter dividing the flow of inert gaseous fluid withentrained water into a first portion and a second portion and directingthe first portion of the flow of inert gaseous fluid with entrainedwater into the liquid capture vessel and directing the second portion ofthe flow of inert gaseous fluid with entrained water to bypass theliquid capture vessel. A flow joiner may be disposed in the inert gasdistribution network downstream with respect to the flow of inertgaseous fluid of the liquid capture vessel, the flow joiner having afirst inlet in fluid flow communication with the liquid capture tank forreceiving a flow of inert gaseous fluid thereform and a second inlet influid flow communication with the flow splitter for receiving the secondportion of the flow of inert gaseous fluid with entrained water and anoutlet for reintroducing the flow of inert gaseous fluid received fromthe liquid capture vessel and the second half of the flow of inertgaseous fluid with entrained water into the inert gas distributionnetwork upstream of the at least one fluid discharge device. In anembodiment, each of the first portion and the second portion constituteabout one-half of the water introduced into the flow of inert gaseous.

In an embodiment of the system, the liquid capture vessel is connectedto the inert gas distribution network upstream with respect to inert gasflow of the connection of the source of water to the inert gasdistribution network, and the source of a secondary liquid is connectedto the inert gas distribution network upstream with respect to inert gasflow of the connection of the liquid capture vessel to the inert gasdistribution network. An inert gas inlet line may be provided toestablish fluid flow communication between the inert gas distributionnetwork and the source of a secondary liquid for pressurizing the sourceof the secondary liquid with pressured inert gas. A flow restrictiondevice may be disposed in the inert gas distribution network upstreamwith respect to inert gas flow of the connection of the source of asecondary liquid to the inert gas distribution network and downstreamwith respect to inert gas flow of the connection of the inert gas inletline to the source of a secondary liquid with the inert gas distributionnetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the invention is to be read inconnection with the accompanying drawing, where:

FIG. 1 is a depiction, partly is schematic and partly in perspective, ofa first exemplary embodiment of a fire suppression system in accord withthe invention; and

FIG. 2 is a depiction, partly is schematic and partly in perspective, ofa second exemplary embodiment of a fire suppression system in accordwith the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is depicted a first exemplary embodimentof a fire suppression system 10 in accord with the invention. The system10 includes one or more vessels 20 for storing an inert gas, that is achemically non-reactive gas, such as for example nitrogen, argon, neon,helium or a mixture of two or more of these gases, a water storagevessel 30, and at least one spray nozzle assembly 45 disposed within thespace to be protected. However, if the space to be protected is large orincludes a number of rooms, a plurality of spray nozzles assemblies 45may be disposed within the space to be protected. Although four spraynozzle assemblies 45 are depicted in the exemplary embodiment of thesystem 10 illustrated in FIG, 1, it will be understood by those skilledin the art that the actual number of spray nozzle assemblies installedin any particular application will depend upon the volume and planararea of the protected space.

The inert gas storage vessels 20 are connected in parallel arrangementin flow communication with the spray nozzle assemblies 45 via an inertgas distribution network made of a supply pipe 15, an intermediatedistribution pipe 17 and a plurality of circuit pipes 19. Each of thecircuit pipes 19 branches off and is in fluid flow communication withthe intermediate distribution pipe 17 and has a terminus disposed withinthe space to be protected to which a respective one of the spray nozzles45 is mounted. The intermediate distribution pipe 17 is also connectedin fluid flow communication with the inert gas supply pipe 15. Each ofthe inert gas storage vessels 20 has its gas outlet connected via abranch supply line 13 in flow communication with the supply pipe 15. Acheck valve 14 may be disposed in each branch supply line 13 forallowing the inert gas to flow from the respective inert gas storagevessel 20 associated therewith through branch supply line 13 into theinert gas supply pipe 15, but not to flow back into the inert gasstorage vessel. Each of the inert gas storage vessels 20 may be equippedwith an outlet valve 16 to regulate the gas discharge pressure. Ifdesired, the outlet valve 16 may also be designed to control the rate ofinert gas flow from the storage vessel associated therewith. As will beexplained in further detail later, when a fire is detected within thespace to be protected, inert gas under pressure within the inert gasvessels 20 passes therefrom through the supply pipe 15 to and throughthe intermediate distribution pipe 17 an thence to and through each ofthe circuit pipes 19 which feed the inert gas to a respective one of thespray nozzle assemblies 45.

The water storage vessel 30 defines an interior volume 32 wherein asupply of water is stored, a gas inlet line 34 and a water outlet line36. The gas inlet line 34 establishes flow communication between theinert gas supply pipe 15 and an upper region of the interior volume 32of the water storage vessel 30. The water outlet line 36 establishesflow communication between a lower region of the water storage vessel 30and the inert gas distribution network at a location downstream withrespect to inert gas flow of the location at which the gas inlet line 34taps into the inert gas supply line 15. Additionally, a flow restrictiondevice 38 is disposed in the inert gas distribution network at alocation between the location upstream thereof at which the gas inletline 34 taps into the supply line 15 and the location downstream thereofat which the water outlet line 36 opens into the inert gas distributionnetwork. The flow restriction device 38, which may comprise for examplea fixed orifice device interdisposed in the inert gas supply line 15,causes a pressure drop to occur as the inert gas traverses the flowrestriction device 38, whereby a gas pressure differential isestablished between the upstream location at which the gas inlet line 34taps into the inert gas supply pipe 15 and the downstream location atwhich the water outlet line 36 opens into the inert gas distributionnetwork. A spray nozzle 37 may be mounted to the outlet end of the wateroutlet line 36 to atomize or otherwise produce a mist of water dropletsas the water from the supply tank 30 is introduced into the inert gassupply pipe 15 of the inert gas distribution network at a locationdownstream of the flow restriction device 38.

Referring now to the exemplary embodiment of the fire suppression system10 depicted in FIG. 1, the fire suppression system 10 includes a flowsplitter 40 and a liquid capture vessel 50. The flow splitter 40 has aflow splitting tee 46 and a flow joining tee 48 and a pair of lines 42and 44 defining parallel flow paths. The flow splitter 40 isinterdisposed in the gas supply pipe 15 at a location downstream withrespect to inert gas flow of the location at which the water outlet line36 opens into the inert gas supply pipe 15. The flow splitting tee 46has an inlet opening upstreamwardly in flow communication to the inertgas supply pipe 15, a first outlet leg opening downstreamwardly in flowcommunication with the liquid capture vessel 50 and a second outlet legopening downstreamwardly in flow communication with the flow line 44 ofthe flow splitter 40. The flow joining tee 48 has an outlet openingdonwstreamwardly in flow communication to the inert gas supply pipe 15,a first inlet leg opening upstreamwardly in flow communication with theflow line 42 of the flow splitter 40 and a second inlet leg openingupstreamwardly in flow communication with the flow line 44 of the flowsplitter 40. In operation, a two-phase flow of water and inert gaspassing through the inert gas supply pipe 15 enters into the flowsplitting tee 46 and self divides into a first fluid flow passingthrough the first outlet leg and a second fluid flow passing through thesecond outlet leg. The first and second fluid flows are substantiallyequal in mass flow rate.

The liquid capture vessel 50 defines an interior chamber 55 and has aninlet line 52 opening at its first end in fluid flow communication withthe first outlet leg of the flow splitting tee 46 and opening at itssecond end into the interior chamber 55 to establish flow communicationbetween the flow splitter 40 and the interior chamber 55 of the liquidcapture vessel 50. The first fluid flow of the two-phase fluid passingthrough the flow splitting tee 46 pass into and through the inlet line52 to enter the interior chamber 55 of the liquid capture vessel 50. Asthe two phase fluid flow passes out the second end of the inlet line 52into the interior chamber 55, it strikes an impact plate 58 disposedwithin the interior chamber 55 in opposition to the outlet of the inletline 52 causing most of the water within the two phase fluid flow toseparate from the two phase flow. The separated water coalesces anddrains into and collects in the lower portion of the interior chamber 55of the liquid capture vessel 50.

The liquid capture vessel 50 also has an outlet line 54 opening at itsfirst end into an upper portion of the interior chamber 55 of the liquidcapture vessel 50 and opening at its outlet end in fluid flowcommunication with the first fluid flow line 42 of the flow splitter 40.The inert gas portion of the first fluid flow passing into the interiorchamber 55 of the liquid capture vessel 50 collects within the interiorchamber 55 above the water separated therefrom which collects in thelower portion of the interior chamber 55. The first fluid flow, whichnow constitutes a flow of inert gas with only a minor amount of thewater originally mixed therewith, passes from the interior chamber 55through outlet line 54 into and through the first flow line 42 of thesplitter 40 into the first inlet leg of the flow joining tee 48. Thesecond fluid flow, which still constitutes a flow of inert gascontaining the water originally mixed therewith, passes through thesecond flow line 44 into the second inlet leg of the flow joining tee48. The flow areas of the respective legs of the flow splitting tee 46and the flow joining tee 48 are sized such that the correct ratio ofwater to inert gas is achieved for optimum fire extinguishing via gasflooding. The first and second fluid flows reunite and pass from theflow joining tee 48 into and through the inert gas supply pipe 15,thence through the intermediate distribution line 17, and thence throughthe several circuit lines 19 to be emitted into the protected space viathe respective spray nozzles 40.

In this embodiment of the invention illustrated in FIG. 1, an excessamount of water is added to the inert gas flow upstream of the flowsplitter 40 and subsequently removed from the inert gas flow at theliquid capture vessel 50, which is positioned upstream of theintermediate distribution line 17. Therefore, the inert gas flow emittedinto the protected space contains only a limited amount of water, thatlimited amount of water being sufficient to increase the heat absorptioncapacity of inert gas flow, but insufficient to alter the floodingcharacteristic of the inert gas flow. If the excess water were notremoved from the inert gas flow, but rather emitted therewith into theprotected space through the spray nozzles 40, the floodingcharacteristic of the fire suppression system of the invention would beimpaired and the system would function more like a water misting system.

As noted previously, the inert gas passing through the inert gas supplypipe 15 has a very low temperature, typically a temperature in the rangeof −60 degrees C. to −100 degrees C. The water, however, mixed into theinert gas flow is stored within the water storage tank 60 at roomtemperature of about 20 degrees C. If the water storage tank 60 islocated outdoors or in an unheated space, the water may be heatedsufficiently, typically to a temperature in the range of 20 to 80degrees C. to ensure that the water within the water storage tank 60does not freeze. During the time in which the excess water is entrainedin the inert gas flow as it passes through the gas supply pipe 15, thewater entrained therein is cooled as its losses heat to the inert gas inwhich it is entrained.

The water introduced into the inert gas flow possesses a thermal inertiawhich delays freezing of the water due to heat loss to the cold inertgas. As used herein, the thermal inertia, TI, of a fluid may berepresented simply as the product of the specific heat capacity, c_(P),of the fluid and the temperature differential between the fluid storagetemperature, T_(S), and the freezing point temperature, T_(F), of thefluid, that is by the formula:

TI=c _(p)(T _(S) −T _(F)).

Based on its specific heat capacity and the 20 degree C. differentialbetween its storage temperature and its freezing point, the waterpossesses a thermal inertia of about 84 Joules per gram. The excesswater is in effect a “cold sink” in that the excess water providesadditional thermal inertia useful to heat the inert gas and is thensubsequently removed from the system. Due to the presence of the excesswater, the limited amount of water that is retained in the inert gasflow and emitted into the protected space with the inert gas is notcooled to as low a temperature as it would be but for the additionalthermal inertia provide by the excess water admixed with the inert gasflow and subsequently removed from the system. Therefore, the limitedamount of water retained in the inert gas and emitted through the spraynozzles 40 into the protected space does not freeze into ice, butremains as a liquid.

Thus, sufficient water must be admixed with the inert gas flow at alocation upstream of the flow splitter 40 to ensure that the thermalcapacity of the overall amount of water added to the inert gas flow issufficient to raise the temperature of the resultant two-phase fluidabove 0 degrees C. For example, water may be admixed with the inert gasflow at a mass flow ratio of water to inert gas of about 1:2 upstream ofthe flow splitter 40 to add sufficient thermal capacity to raise theresultant two phase flow to a temperature above 0 degrees C.Approximately one-half of that water may then be removed at the flowsplitter 40 and collected in the water storage vessel 50 to reduce themass flow ratio of water to inert gas to about 1:4 downstream of theflow splitter 40 to ensure that the amount of water emitted into theprotected space with the inert gas flow is limited so as not to destroythe “flooding” characteristic of the inert gas flow of the firesuppression inerting system 10 depicted in FIG. 1.

Referring now to FIG. 2, in the exemplary embodiment of the firesuppression system 10 depicted therein, a secondary liquid is admixedwith the inert gas flow, rather than an excess amount of water, as aheat exchange medium for heating the inert gas flow. In this embodiment,in addition to the water storage tank 30, the fire suppression system 10includes a secondary liquid storage vessel 60 and a secondary liquidcapture vessel 70, both disposed upstream with respect to inert gas flowof the water storage tank 30. The secondary liquid storage vessel 60defines an interior volume 62 wherein a supply of the secondary liquidis stored. A gas inlet line 64 connects the inert gas supply pipe 15 influid communication with the interior chamber 62 of the secondary liquidstorage vessel 60. A secondary liquid outlet line 66 establishes fluidflow communication between a lower region of the interior chamber 62 ofthe secondary liquid storage vessel 60 and the inert gas distributionnetwork at a location upstream with respect to inert gas flow of thelocation at which the inert gas inlet line 34 to the water storagevessel 30 taps into the inert gas supply pipe 15. Additionally, a flowrestriction device 68 is disposed in the inert gas distribution networkat a location between the location upstream thereof at which the gasinlet line 64 to the secondary liquid storage vessel 60 taps into theinert gas supply line 15 and the location downstream thereof at whichthe secondary liquid outlet line 66 from the secondary liquid storagevessel 60 taps into the inert gas supply line 15. The flow restrictiondevice 68, which may comprise for example a fixed orifice deviceinterdisposed in the inert gas supply line 15, causes a pressure drop tooccur as the inert gas traverses the flow restriction device 68, wherebya gas pressure differential is established between the upstream locationat which the gas inlet line 64 taps into the inert gas supply pipe 15and the downstream location at which the secondary liquid outlet line 66from the secondary liquid storage vessel 60 opens into the inert gasdistribution network.

The secondary liquid capture vessel 70 defines an interior chamber 75and has an inlet line 72 opening at its inlet end in fluid flowcommunication with the upstream portion 15 a the inert gas supply pipe15 at a location downstream with respect to fluid flow therethrough ofthe location at which the secondary liquid outlet line 66 taps into theinert gas supply pipe 15 and opening at its outlet end into a lowerportion of the interior chamber 75 of the secondary liquid capturevessel 70. The upper portion of the interior chamber 75 of the secondaryliquid capture vessel 70 is in fluid flow communication with thedownstream portion 15 b of the inert gas supply pipe 15. Thus, in thisembodiment, the interior chamber 75 of the secondary liquid capturevessel 70 is interdisposed in the fluid flow path defined by the inertgas supply pipe 15 of the inert gas distribution network.

In the FIG. 2 embodiment, when a fire is detected in the protectedspace, inert gas is released from the inert gas storage vessels 20 intothe inert gas supply pipe 15 and thence through the intermediatedistribution line 17 and the respective branch lines 19 to be emittedthrough the spray nozzles 45 into the protected space. As the inert gasflow traverses the supply pipe 15, a portion of the inert gas passesthrough the inlet line 64 to pressurize the interior chamber 62 of thesecondary liquid storage vessel 60. The pressurization of the interiorchamber 62 of the secondary liquid storage vessel 60 forces secondaryliquid therein to pass out of the interior chamber 62 through the outletline 66 and into the inert gas supply pipe 15 at a location downstreamof the flow restriction device 68 to mix with the inert gas flowingthrough the inert gas supply pipe 15 and form a two-phase flow.

As this two-phase flow continues to flow downstream through the inertgas supply pipe 15, the droplets of the secondary liquid intermix withthe inert gas and transfer heat to the colder inert gas. At a locationupstream with respect to inert gas flow of the water storage tank 30,the two-phase mixture of secondary liquid and inert gas flowing throughthe inert gas supply pipe 15 passes into the secondary liquid capturevessel 70 through the inlet line 72. As the two-phase fluid exits theoutlet end of the inlet line 72 into the interior chamber 75, it strikesan impact plate 78 disposed within the interior chamber 75 in oppositionto the outlet end of the inlet line 72 causing most of the liquiddroplets of secondary liquid to coalesce. The captured secondary liquidthen drains into and collects in the lower portion of the interiorchamber 75 of the liquid capture vessel 70. The inert gas, however,collects in the upper portion of the secondary liquid capture vessel 70above the secondary liquid collecting in the lower portion of the vessel70 and passes therefrom into the downstream portion 15 b of the inertgas supply pipe 15.

In this embodiment of the fire suppression system 10, the fireextinguishing water is introduced into the inert gas flow passingthrough the inert gas supply pipe 15 downstream with respect to inertgas flow of the location at which the inert gas re-enters into the inertgas supply pipe 15 from the secondary liquid capture vessel 70.Referring still to FIG. 2, the gas inlet line 34 establishes flowcommunication between the inert gas supply pipe 15 and an upper regionof the interior volume 32 of the water storage vessel 30. The wateroutlet line 36 establishes flow communication between a lower region ofthe water storage vessel 30 and the inert gas distribution network at alocation downstream with respect to inert gas flow of the location atwhich the gas inlet line 34 taps into the inert gas supply line 15. Asin the FIG. 1 embodiment, a flow restriction device 38 is disposed inthe inert gas distribution network at a location between the locationupstream thereof at which the gas inlet line 34 taps into the supplyline 15 and the location downstream thereof at which the water outletline 36 opens into the inert gas distribution network. As notedpreviously, when the interior chamber 32 of the water storage vessel 30is pressurized by inert gas passing through inert gas inlet line 34 fromthe inert gas supply pipe 15, water is forced through the water outletline 36 and into the inert gas flow passing through the inert gas supplyline 15. A spray nozzle 37 may be mounted to the outlet end of the wateroutlet line 36 to atomize or otherwise produce a mist of water dropletsas the water from the supply tank 30 is introduced into the inert gasflow.

Although the secondary liquid that serves as the thermal inertia sourcefor heating the inert gas may be water, it is contemplated that otherfluids having a greater thermal range of operation (i.e. a freezingpoint lower than 0° C.) and/or a greater heat capacity. Additionally,since substantially all of the secondary liquid is captured and removedfrom the system prior to the addition the water into the inert gas flow,the amount secondary liquid introduced into the inert gas may beoptimized for a given application without concern that excess watermight adversely affect the “flooding” effect of the inert gas asdiscussed hereinbefore. Further, the limited amount of water added toinert gas flow to augment the fire-extinguishing capacity of the inertgas flow, but not adversely affecting the “flooding” effect of the inertgas, may be independently determined as desired. Also, since thesecondary liquid is removed in the capture vessel 70 and does notparticipate in fire extinguishment, the secondary liquid need not haveany fire extinguishing capacity.

The thermal inertia, TI, provided by the secondary liquid may berepresented simply as the product of the specific heat capacity, C_(P),of the secondary liquid and the temperature differential between thesecondary liquid storage temperature, T_(S), and the freezing pointtemperature, T_(F), of the secondary liquid, that is by the formula:

TI=c _(P)(T _(S) −T _(F)).

For example, a saturated solution of potassium lactate, which has afreezing point temperature of −55 degrees C., would make an excellentsecondary liquid. Assuming that a saturated solution of potassiumlactate would have a specific heat capacity similar to that of water,the thermal inertia per gram of a saturated solution of potassiumlactate stored at room temperature would be about 315 Joules per gram,which is substantially greater than the thermal inertia per gram ofwater at room temperature.

It is to be understood that other liquids having a thermal inertiagreater than that of water may also be used as the secondary liquid incarrying out the invention. Any liquid having a lower freezing pointthan water and the same specific heat capacity as water would provide agreater thermal inertia per gram than water. Any liquid having a higherspecific heat capacity than water and the same freezing pointtemperature as water would also provide a greater thermal inertia pergram than water. An advantage of using a liquid having such a higherthermal inertia as the secondary liquid is that much less secondaryliquid would need to be used to prevent freezing of the limited amountof fire-extinguishing water introduced into the inert gas. This in turnwould reduce the cost of the system by reducing the storage volumerequired for the storage volume need for storing the secondary liquid.

Although the present invention has been described with reference to oneor more exemplary embodiments, it will be recognized by those skilled inthe art that various modifications may be made without departing fromthe scope of the appended claims. Therefore, it is intended that theembodiments presented herein not be construed as limiting the scope ofthe invention, but rather that the invention be defined by the fullscope of the appended claims, including without limitation anyequivalents that may be accorded under applicable law.

1. A method of extinguishing a fire in a protected space, said methodcomprising the steps of: passing a flow of inert gaseous fluid to atleast one discharge device operatively associated with the protectedspace; introducing a first amount of water into said flow of inertgaseous fluid upstream of the at least one discharge device; introducinga second amount of a secondary liquid into said flow of inert gaseousfluid for heating said flow of inert gaseous fluid; and removing saidsecond amount of said secondary liquid from said flow of inert gaseousfluid upstream of the at least one discharge device.
 2. A method asrecited in claim 1 wherein the step of introducing a second amount of asecondary liquid into said flow of inert gaseous fluid comprisesintroducing a second amount of water into said flow of inert gaseousfluid.
 3. A method as recited in claim 2 wherein said second amount ofwater introduced into said flow of inert gaseous fluid at about roomtemperature.
 4. A method as recited in claim 2 wherein said first amountof water and said second amount of water are introduced into said flowof inert gaseous fluid as a single amount of water.
 5. A method asrecited in claim 4 wherein said step of removing said second amount ofsaid secondary liquid from said flow of inert gaseous fluid upstream ofthe at least one discharge device comprises removing about one-half ofthe single amount of water introduced into said flow of inert gaseousfluid upstream of the at least one discharge device.
 6. A method asrecited in claim 1 wherein the step of introducing a second amount of asecondary liquid into said flow of inert gaseous fluid comprisesintroducing a second amount of a secondary liquid having a high thermalinertia into said flow of inert gaseous fluid upstream with respect tothe flow of inert gaseous fluid of introducing a first amount of waterinto said flow of inert gaseous fluid.
 7. A method as recited in claim 6wherein the step of removing said second amount of said secondary liquidfrom said flow of inert gaseous fluid upstream of the at least onedischarge device comprises removing said secondary liquid from said flowof inert gaseous fluid upstream with respect to the flow of inertgaseous fluid of introducing a first amount of water into said flow ofinert gaseous fluid and downstream with respect to the flow of inertgaseous fluid of introducing a second amount of a secondary liquid intosaid flow of inert gaseous fluid.
 8. A method as recited in claim 1wherein the step of introducing a second amount of a secondary liquidinto said flow of inert gaseous fluid comprises introducing a secondamount of a secondary liquid having a specific heat capacity at leastabout equal to the specific heat capacity of water and a freezing pointtemperature less than 0° C. into said flow of inert gaseous fluidupstream with respect to the flow of inert gaseous fluid of introducinga first amount of water into said flow of inert gaseous fluid.
 9. Amethod as recited in claim 8 wherein the step of removing said secondamount of said secondary liquid from said flow of inert gaseous fluidupstream of the at least one discharge device comprises removing saidsecondary liquid from said flow of inert gaseous fluid upstream withrespect to the flow of inert gaseous fluid of introducing a first amountof water into said flow of inert gaseous fluid and downstream withrespect to the flow of inert gaseous fluid of introducing a secondamount of a secondary liquid into said flow of inert gaseous fluid. 10.A method as recited in claim 1 wherein the step of introducing a secondamount of a secondary liquid into said flow of inert gaseous fluidcomprises introducing a second amount of a secondary liquid into saidflow of inert gaseous fluid upstream with respect to the flow of inertgaseous fluid of introducing a first amount of water into said flow ofinert gaseous fluid, and the step of removing said second amount of saidsecondary liquid from said flow of inert gaseous fluid upstream of theat least one discharge device comprises removing said secondary liquidfrom said flow of inert gaseous fluid downstream with respect to theflow of inert gaseous fluid of introducing a second amount of asecondary liquid into said flow of inert gaseous fluid and upstream withrespect to the flow of inert gaseous fluid of introducing a first amountof water into said flow of inert gaseous fluid.
 11. A method as recitedin claim 10 wherein said secondary liquid comprises a saturated solutionof potassium lactate.
 12. A fire suppression system for extinguishing afire in a protected space comprising: a source of pressurized inertgaseous fluid; at least one fluid discharge device disposed in operativeassociation with the protected space; an inert gas distribution networkfor directing a flow of the inert gaseous fluid from said source ofpressurized inert gaseous fluid to said at least one discharge devicefor emission into the protected space; a source of water, said source ofwater connected in fluid flow communication with said inert gasdistribution network for introducing water from said source of waterinto the flow of inert gaseous fluid; a source of a secondary liquidhaving a thermal inertia for heating the flow of inert gaseous fluid,said source of the secondary liquid connected in fluid flowcommunication with said inert gas distribution network for introducingthe secondary liquid into the flow of inert gaseous fluid; and a liquidcapture vessel for removing the secondary liquid from the flow of inertgaseous fluid, said liquid capture vessel connected in fluid flowcommunication with said inert gas distribution network downstream withrespect to the flow of inert gaseous fluid of the connection of saidsource of a secondary liquid to said inert gas distribution network andupstream with respect to the flow of inert gaseous fluid of the at leastone fluid discharge device.
 13. A fire suppression system as recited inclaim 12 wherein said secondary liquid comprises water.
 14. A firesuppression system as recited in claim 13 wherein said source of waterand said source of a secondary liquid are a single source.
 15. A firesuppression system as recited in claim 14 wherein said liquid capturetank removes about one-half of the water introduced into the flow inertgaseous fluid form the flow of inert gaseous fluid with entrained waterupstream with respect to the flow of inert gaseous fluid of the at leastone fluid discharge device.
 16. A fire suppression system as recited inclaim 14 further comprising a flow splitter disposed in said inert gasdistribution network downstream with respect to the flow of inertgaseous fluid of the connection of said single source of water to saidinert gas distribution network and upstream with respect to the flow ofinert gaseous fluid of said liquid capture vessel, said flow splitterdividing the flow of inert gaseous fluid with entrained water into afirst half and a second half and directing said first half of the flowof inert gaseous fluid with entrained water into said liquid capturevessel and directing said second half of the flow of inert gaseous fluidwith entrained water to bypass said liquid capture vessel.
 17. A firesuppression system as recited in claim 16 further comprising a flowjoiner disposed in said inert gas distribution network downstream withrespect to the flow of inert gaseous fluid of said liquid capturevessel, said flow joiner having a first inlet in fluid flowcommunication with said liquid capture tank for receiving a flow ofinert gaseous fluid thereform and a second inlet in fluid flowcommunication with said flow splitter for receiving the second half ofthe flow of inert gaseous fluid with entrained water and an outlet forreintroducing the flow of inert gaseous fluid received from the liquidcapture vessel and the second half of the flow of inert gaseous fluidwith entrained water into said inert gas distribution network upstreamof said at one fluid discharge device.
 18. A fire suppression system asrecited in claim 12 wherein: said liquid capture vessel is connected tosaid inert gas distribution network upstream with respect to inert gasflow of the connection, of said source of water to said inert gasdistribution network; and said source of a secondary liquid is connectedto said inert gas distribution network upstream with respect to inertgas flow of the connection of said liquid capture vessel to said inertgas distribution network.
 19. A fire suppression system as recited inclaim 18 further comprising an inert gas inlet line establishing fluidflow communication between said inert gas distribution network and saidsource of a secondary liquid for pressurizing the source of thesecondary liquid with pressured inert gas.
 20. A fire suppression systemas recited in claim 19 further comprising a flow restriction devicedisposed in said inert gas distribution network upstream with respect toinert gas flow of the connection of said source of a secondary liquid tosaid inert gas distribution network and downstream with respect to inertgas flow of the connection of said inert gas inlet line to said sourceof a secondary liquid with the inert gas distribution network.
 21. Afire suppression system as recited in claim 18 wherein said source of asecondary liquid comprises a tank containing a saturated solution ofpotassium lactate.
 22. A fire suppression system for extinguishing afire in a protected space comprising: a source of pressurized inertgaseous fluid; at least one fluid discharge device disposed in operativeassociation with the protected space; an inert gas distribution networkfor directing a flow of the inert gaseous fluid from said source ofpressurized inert gaseous fluid to said at least one discharge devicefor emission into the protected space; a source of a liquid fireextinguishing agent, said source of liquid fire extinguishing agentconnected in fluid flow communication with said inert gas distributionnetwork for introducing liquid fire extinguishing agent from said sourceof liquid fire extinguishing agent into the flow of inert gaseous fluid;a source of a secondary liquid having a thermal inertia for heating theflow of inert gaseous fluid, said source of the secondary liquidconnected in fluid flow communication with said inert gas distributionnetwork for introducing the secondary liquid into the flow of inertgaseous fluid; and a liquid capture vessel for removing the secondaryliquid from the flow of inert gaseous fluid, said liquid capture vesselconnected in fluid flow communication with said inert gas distributionnetwork downstream with respect to the flow of inert gaseous fluid ofthe connection of said source of a secondary liquid to said inert gasdistribution network and upstream with respect to the flow of inertgaseous fluid of the at least one fluid discharge device.
 23. A methodof extinguishing a fire in a protected space, said method comprising thesteps of: passing a flow of inert gaseous fluid to at least onedischarge device operatively associated with the protected space;introducing a first amount of a liquid fire extinguishing agent intosaid flow of inert gaseous fluid upstream of the at least one dischargedevice; introducing a second amount of a secondary liquid into said flowof inert gaseous fluid for heating said flow of inert gaseous fluid; andremoving said second amount of said secondary liquid from said flow ofinert gaseous fluid upstream of the at least one discharge device.
 24. Amethod of extinguishing a fire in a protected space substantially ashereinbefore described with reference to any one of the accompanyingdrawings.
 25. A fire suppression system for extinguishing a fire in aprotected space substantially as hereinbefore described with referenceto any one of the accompanying drawings.